Many in the education world talk about the power of expectations, expressing the belief that if adults in a school expect students to succeed, then students will rise to that expectation, and if adults expect failure — well, that, too, can be a self-fulfilling prophecy.

Now a new study suggests that race plays a big role in influencing how teachers see their students’ potential for academic success, raising questions about whether teachers’ biases could be holding back black students and contributing to the nation’s yawning achievement gap.

When a white (or other non-black) teacher and a black teacher evaluate the same black student, the study found, the white teacher is 30 percent less likely to believe that the student will graduate from a four-year college — and 40 percent less likely to believe the student will graduate from high school.

“What we find is that white teachers and black teachers systematically disagree about the exact same student,” Nicholas Papageorge, a Johns Hopkins economist and co-author of the study, said in a statement.

“If I’m a teacher and decide that a student isn’t any good, I may be communicating that to the student,” Papageorge said. “A teacher telling a student they’re not smart will weigh heavily on how that student feels about their future and perhaps the effort they put into doing well in school.”

The data came from the Education Longitudinal Study of 2002, which was conducted by the statistics and research arm of the U.S. Education Department. The study asked math and reading teachers of high school sophomores to predict how far each of their students would go in school.

It adds to a growing body of evidence that race affects how teachers see and treat their students. Black students taught by white teachers are less likely to be identified for gifted programs than black students taught by black teachers, for example. Other research has shown biases in teachers’ grading of work by students of different genders, races and ethnicities.

Such research has bolstered calls from all corners of the education world — including the Education Department, teachers unions and Teach for America — to boost diversity among the nation’s teachers.